Search found 2590 matches

by tomfid
Fri Apr 26, 2019 7:01 pm
Forum: Vensim
Topic: Running with Different Timesteps
Replies: 16
Views: 418

Re: Running with Different Timesteps

No (except perhaps for some complex tricks). What are you trying to do?
by tomfid
Fri Apr 26, 2019 1:50 pm
Forum: Vensim
Topic: Using Time Steps
Replies: 5
Views: 171

Re: Using Time Steps

Not following this ... if variable #2 only has an initial value, how can new values be measured?
by tomfid
Fri Apr 26, 2019 1:19 pm
Forum: Vensim
Topic: Defining Units
Replies: 4
Views: 137

Re: Defining Units

Definitely - percent is important because it's easy to inadvertently mix % and fractions. Define a variable called "100 percent" with units of "percent" and use that to convert between the two. Something like: "100 percent" == 100 ~ percent birth rate = 2.3 ~ percent/year fractional birth rate = bir...
by tomfid
Thu Apr 25, 2019 3:18 pm
Forum: Vensim
Topic: How to count number of storage cycle
Replies: 2
Views: 124

Re: How to count number of storage cycle

The word "count" implies "stock". You can do something like the following: count = INTEG( counting, 0 ) counting = start of cycle/TIME STEP start of cycle = {logical flag - a function of your process} The trick is to avoid counting the same cycle in consecutive TIME STEPS, but it's hard to say more ...
by tomfid
Wed Apr 24, 2019 4:27 pm
Forum: Vensim
Topic: accumulate auxillary values
Replies: 4
Views: 142

Re: accumulate auxillary values

What you choose depends on what you need to represent - if you're modeling an accounting process explicitly, the pulsed or delayed reporting stock is good. If you're just capturing the natural delay and smoothing in a perception process, it's much simpler to use a SMOOTH or SMOOTH3 function. Reporti...
by tomfid
Wed Apr 24, 2019 3:15 pm
Forum: Vensim
Topic: accumulate auxillary values
Replies: 4
Views: 142

Re: accumulate auxillary values

You can use a stock to keep track of this. Make the inflow the current death rate, and the outflow equal to a DELAY FIXED of the same rate, with a time constant of one year (in whatever units your model is using).
by tomfid
Mon Apr 22, 2019 1:12 pm
Forum: Vensim
Topic: Random Weibull Distribution Parameters
Replies: 1
Views: 116

Re: Random Weibull Distribution Parameters

See the sample model at the end of viewtopic.php?f=2&t=6892 (April 18).
by tomfid
Thu Apr 18, 2019 6:16 pm
Forum: Vensim
Topic: Questions about random Weibull
Replies: 15
Views: 1377

Re: Questions about random Weibull

Here are three different parameterizations, using terminology from NIST, Wikipedia and Wolfram Mathworld:
RANDOM functions.mdl
(38.93 KiB) Downloaded 16 times
by tomfid
Wed Apr 17, 2019 9:26 pm
Forum: Vensim
Topic: Questions about random Weibull
Replies: 15
Views: 1377

Re: Questions about random Weibull

Try the sample model attached to the help system topic for the random functions. It's in c:\users\public\vensim if your OS won't let the help link work.
by tomfid
Wed Apr 17, 2019 8:03 pm
Forum: Vensim
Topic: Questions about random Weibull
Replies: 15
Views: 1377

Re: Questions about random Weibull

Terminology for the Weibull distribution is not well standardized, and most sources don't use alpha and beta. Can you give us a reference you're trying to match?
by tomfid
Wed Apr 17, 2019 12:57 pm
Forum: Vensim
Topic: Running multiple models
Replies: 3
Views: 139

Re: Running multiple models

It sounds like you're running a chain of models, where the output from one is the input to the next. This is easy with a command script (requires Vensim DSS).
by tomfid
Mon Apr 15, 2019 1:49 pm
Forum: Vensim
Topic: Hearne' method
Replies: 2
Views: 132

Re: Hearne' method

I assume you mean this? https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1939-7445.2009.00058.x The paper is paywalled, but I'm going to speculate that in general it would be tricky to implement. You'd have to have a library of functions with desired properties that meet all the reality checks need...
by tomfid
Mon Apr 08, 2019 9:19 pm
Forum: Vensim
Topic: Read in time-dependent array from Excel
Replies: 1
Views: 133

Re: Read in time-dependent array from Excel

If you're using GET XLS, it can only handle one dimension (plus time) at a time. So, you'd need three equations to import this: data[USA,importCountries] = GET XLS DATA( ... , 'C5' ) data[Germany,importCountries] = GET XLS DATA( ... , 'C8' ) data[China,importCountries] = GET XLS DATA( ... , 'C11' ) ...
by tomfid
Mon Apr 08, 2019 9:05 pm
Forum: Vensim
Topic: Varformat error 1071225242
Replies: 12
Views: 300

Re: Varformat error 1071225242

Great - hopefully things can move forward now.
by tomfid
Mon Apr 08, 2019 8:09 pm
Forum: Vensim
Topic: Varformat error 1071225242
Replies: 12
Views: 300

Re: Varformat error 1071225242

Global_model-mod+biogeochem.mdl
(602.96 KiB) Downloaded 14 times
This is a working merger (it parses and runs, but crashes with an fp error pretty quickly). I had to modify the equations differently - modifying the host global model's j and k ranges rather than the biogeochem model.
by tomfid
Mon Apr 08, 2019 6:52 pm
Forum: Vensim
Topic: Varformat error 1071225242
Replies: 12
Views: 300

Re: Varformat error 1071225242

Was the modified BIOGEOCHEM model runnable before you attempted the paste? It appears that it uses a lot of individual subscript elements in the equations, so it would be nontrivial to rename the elements.
by tomfid
Mon Apr 08, 2019 5:02 pm
Forum: Vensim
Topic: Varformat error 1071225242
Replies: 12
Views: 300

Re: Varformat error 1071225242

I think part of the problem may be that you have j and k ranges in both models, presumably with different ranges and interpretations. Since the biogeochem model is simpler, I'd rename all the ranges, subranges and elements there before doing the copy/paste. In any case, i, j, k etc. would usually be...
by tomfid
Mon Apr 08, 2019 4:51 pm
Forum: Vensim
Topic: Varformat error 1071225242
Replies: 12
Views: 300

Re: Varformat error 1071225242

When you paste across models, Vensim generally tries to bring the needed subscript families along. However, if there are overlapping names of elements, ranges or subranges, this may cause a conflict. I think that might be what's happened here. When I look at the subscript control in my copy (in 7.3....
by tomfid
Mon Apr 08, 2019 4:06 pm
Forum: Vensim
Topic: Varformat error 1071225242
Replies: 12
Views: 300

Re: Varformat error 1071225242

I can open the model using File>Edit File to bring it into the text editor. There seem to be a lot of subscript errors: ERROR: Unspecified subscript equation for - j10. ERROR: Unspecified subscript equation for - j11. ERROR: Unspecified subscript equation for - j12. ERROR: Unspecified subscript equa...
by tomfid
Mon Apr 08, 2019 4:03 pm
Forum: Vensim
Topic: Varformat error 1071225242
Replies: 12
Views: 300

Re: Varformat error 1071225242

Do you have an earlier, working version we can compare?
by tomfid
Thu Apr 04, 2019 9:06 pm
Forum: Vensim
Topic: sensitivity analysis (vensim)
Replies: 10
Views: 386

Re: sensitivity analysis (vensim)

Try the samples in the help system: http://vensim.com/documentation/usr15.htm
by tomfid
Thu Apr 04, 2019 9:05 pm
Forum: Vensim
Topic: sensitivity analysis (vensim)
Replies: 10
Views: 386

Re: sensitivity analysis (vensim)

What is shown on this plot? If it's a parameter, it will be constant.
by tomfid
Thu Apr 04, 2019 7:51 pm
Forum: Vensim
Topic: sensitivity analysis (vensim)
Replies: 10
Views: 386

Re: sensitivity analysis (vensim)

Right-click the sensitivity graph tool and change the options to show confidence bounds rather than individual traces.

From your second graph, it looks like the range of behavior is very narrow.
by tomfid
Thu Apr 04, 2019 12:57 pm
Forum: Vensim
Topic: sensitivity analysis (vensim)
Replies: 10
Views: 386

Re: sensitivity analysis (vensim)

Or just Tools>Analysis>New to reload a new copy of the toolset.